The present invention relates to a covering member for a casing of fixed disc memory unit used in computers and other electronic data processing instruments as an external storage medium. More particularly, the invention relates to a covering member for a casing of fixed disc memory unit provided with an air-tight gasket integrally bonded together in advance.
As is well known, many of conventional computers and other data-processing electronic instruments utilize a floppy disc as an external data storage medium. It is a trend in recent years that the floppy discs are increasingly being replaced with fixed disc memory units by virtue of the much larger storage capacity thereof than floppy discs and the much shorter access time for reading-out of the stored information. The above mentioned fixed disc memory is a thin rigid disc usually made of an aluminum alloy and coated with a layer of a magnetic material for magnetic recording. The fixed disc is rotated by means of a spindle motor and a magnetic head held to face the rotating disc keeping a very narrow clearance therebetween of only about 0.5 .mu.m serves to write-in and read-out the magnetically recorded information into and out of the disc.
As is readily understood from the above described working principle of a fixed disc memory, very serious troubles are sometimes caused by dusts entering the clearance between the rotating disc and the magnetic head. Accordingly, it is usual that such a fixed disc is encased together with the spindle motor in an air-tightly sealable casing formed of two covering members of a top cover and a down cover conjoined into the casing by screwing with a gasket member around the peripheral flange of covering member at which it is conjoined with the other covering member. The air inside the casing should be always kept clean or dust-free by means of a filter for internal air circulation and a filter for ventilation with the outer atmosphere.
The above mentioned gasket member used between the top and down covering members is usually prepared to fit the peripheral flange of the covering member by punching a sheet of a foamed or spongy rubber such as silicone rubbers, urethane rubbers, polychloroprene rubbers, NBR rubbers and the like and coated on the surface with a tacky adhesive to facilitate mounting and fixing on the flange of the covering member, optionally, with a release paper applied thereto for providing temporary protection.
The above mentioned procedure of preparation and use of the gasket members of a spongy rubber is very troublesome and economically disadvantageous because a large proportion of the spongy rubber sheet is necessarily wasted after punching of the gasket and gasket members of very accurate dimensions can hardly be obtained by punching a spongy rubber sheet. Moreover, coating of the gasket member with a tacky adhesive and mounting of the gasket member on the correct position of the covering member require great skillfulness of the workers to greatly decrease the productivity. What is worse is that punching of a spongy rubber sheet unavoidably produces a considerable amount of tiny rubber particles which are retained in the open pores of the spongy rubber of the gasket member to be eventually released inside the casing and cause troubles as a kind of dusts. Accordingly, it has been eagerly desired to develop a covering member of casing for a fixed disc memory without the above described problems and disadvantages in the prior art.